1. Field of the Invention
This invention relates to electromagnetic switches and more particularly to electromagnetic switches having a floating magnet with confronting faces contacted by a movable armature having confronting faces, the confronting faces flushly aligning upon contact.
2. Background Information
Electromagnetic switches, also known as contactors or motor starters, are electrically operated switches having an armature and a stationary magnet. The armature is held apart from the stationary magnet by a kick-out spring. Application of electrical energy to a coil within the switch induces the armature to overcome the bias of the kick-out spring. The armature thereby contacts the stationary magnet through magnetic attraction.
Generally, one or more electrically conductive contacts are affixed to the movable armature. Energization of the coil causes the armature to be attracted to and contact the stationary magnet. The electrically conductive contacts of the armature, in turn, touch stationary contacts affixed in the switch housing. Contact touching generally provides a circuit closure for energizing a circuit or a load.
A typical electromagnetic switch is disclosed in U.S. Pat. No. 4,720,763-Bauer. In earlier electromagnetic switches, such as Bauer, the base of the stationary magnet is supported by a wire bail. The stationary magnet, in prior art designs, resides between the bail and a solid fixed support. Although somewhat resilient, the bail provided a stiff impediment to movement by the magnet upon contacting by the movable armature. Upward vertical movement of the magnet is limited by its contact with a solid magnet support piece. This prior art design is responsible for producing secondary bounce between the electrical contacts of the switch.
A number of mechanisms can be involved to cause secondary bounce. A first mechanism is misalignment of the confronting faces of the armature and stationary magnet upon contact. This misalignment can occur in any of three dimensions. The relatively fixed position of the stationary magnet within the housing prevents the stationary magnet from moving to properly align the confronting faces of the stationary magnet with the armature. The movable armature, however, may more freely rotate in any of three dimensions. The movable armature will therefore tend to move in the dimension necessary so that the confronting faces of the armature and magnet flushly align. The electrically conductive contacts, however, are affixed to the movable armature. Movement of the armature after initially contacting the stationary magnet will move the contacts affixed to the armature relative to the stationary contacts affixed in the switch housing. Movement of the contacts after initial contact closure is secondary bounce.
Another form of secondary bounce can occur when the stationary magnet returns to its initial position after being struck by the movable armature. When the coil of the armature is energized, the armature will strike the stationary magnet. Although the bail provides stiff support to the base of the stationary magnet, it is somewhat resilient. The stationary magnet will therefore displace relative to the solid support piece when contacted by the movable armature. The displaced bail will forcefully return the stationary magnet to its original position abutting the solid support surface. The impact of the stationary magnet on the solid support surface can jar the movable armature confronting faces out of flush alignment with the confronting faces of the stationary magnet. The magnetic field between the movable armature and stationary magnet will induce the movable armature to rotate as necessary to cause the confronting faces of the armature to align with the stationary magnet. The contacts affixed to the movable armature will thereby bounce across the stationary contacts in the switch housing producing secondary bounce.
Secondary bounce is an undesirable condition which reduces the electrical life of the electrically conductive contacts due to friction, arcing, and excessive pounding. Furthermore, the unstable current flow path provided by bouncing contacts can adversely affect the waveform of the electrical signal carried by the contacts through the circuit.
There is a need therefore for an electromagnetic switch which eliminates secondary bounce by providing a floating magnet which can rotate upon contact with a movable armature thereby aligning the confronting faces of the magnet with the confronting faces of the armature without a need for movement by the armature.